Use Lambda to create static inner functions?

Question

Is it possible to create static inner function using lambda?

Specifically, I want to do the following:

function myFunc(){
    Map<Integer, String> myMap = new HashMap <Integer, String> ();
    myMap.put(1,"A");
    String head = () -> myMap.get(1);
    myMap.put(1,"B");

    System.out.println(head);   // Should print B
}

What exactly are you trying to do? What's stopping you from calling System.out.println(myMap.get(1))? — shmosel
– shmosel, Commented Mar 9, 2015 at 5:57
Nothing. The idea is to be able to re-use the code so I don't have to rewrite it twice. — Bill Software Engineer
– Bill Software Engineer, Commented Mar 9, 2015 at 5:58
Well in this example, myMap.get(1). But you can imagine any code could go in there. — Bill Software Engineer
– Bill Software Engineer, Commented Mar 9, 2015 at 5:59
@YongkeBillYu No, we can't imagine it. Your example doesn't demonstrate what you are actually trying to do and doesn't even have type consistency. — JLRishe
– JLRishe, Commented Mar 9, 2015 at 6:01

Vitruvie · Accepted Answer · 2015-03-09 06:14:46Z

4

All lambdas are inner functions. The one you wrote is a Supplier<String>:

Supplier<String> getHead = () -> myMap.get(1);
System.out.println(getHead.get());

You can see what types of functions exist by looking through the java.util.function package.

Note however that the standard way to accomplish this (since before lambdas) is simply to write a private method and call it, and the traditional style will have less overhead involved, though whether that overhead is significant is another question.

edited Mar 9, 2015 at 6:14

answered Mar 9, 2015 at 6:01

Vitruvie

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4 Comments

Bill Software Engineer Over a year ago

It works, although it's not as elegant as I had hoped. Maybe the traditional method is better.

JLRishe Over a year ago

@YongkeBillYu There are times when lambda functions are useful and I don't think this is one of those times. Using them to do Supplier<String> getHead = () -> myMap.get(1); instead of String head = myMap.get(1); seems completely pointless to me, so yes, the "traditional method" would be better in this case.

Vitruvie Over a year ago

@JLRishe The point is to call .get() multiple times so that it's like a dynamic variable.

Bill Software Engineer Over a year ago

@Saposhiente Yeah, if you Java could implement Properties like in C# then all this could be avoided, alas!

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